1. Field of the Invention
The present invention generally relates to an adjustable compact high-frequency-high-voltage power supply and, more particularly, to a compact high-frequency-high-voltage power supply utilizing an inverter to convert low-voltage DC power to high-voltage-high-frequency AC power and provide high-frequency-high-voltage AC power at different frequencies and voltages via continuous adjustment of variable resistors during operation.
2. Description of the Prior Art
Inverters are widely used in switching power supplies and inverter motor controllers. The operation frequency of the former is limited within a smaller range because the objective of the former is to provide a stable power to a load. The operation frequency of the latter has to be changed smoothly by using complicated control circuitry so as to change the rotating speed and torque for matching the operation condition and load.
U.S. Pat. No. 4,281,374 discloses a circuit that can output high-voltage AC power so as to convert DC power to an adjustable and waveform-controllable high-voltage AC power using pulse-width modulation (PWM) according to a 600-Hz waveform generator producing a high-frequency waveform and measuring the output AC voltage for feedback control. U.S. Pat. No. 4,281,374 teaches the cutting frequency for PWM generated by a high-frequency oscillator at least ten times the frequency of output AC power. However, the “374” patent does not disclose how to change the cutting frequency for PWM.
U.S. Pat. No. 6,819,061 discloses a power supply apparatus for light source in which AC power is rectified to DC power, converted to high-frequency AC power by use of a DC inverter and then rectified to output DC power. It depends on the comparison between the actual output DC power and a reference power value for keeping a stable output DC power. Moreover, the output DC power is controlled according to the supplied AC voltage so as to prevent over-current due to voltage drop. However, the “061” patent does not teach how to change the frequency of the DC inverter.
U.S. Pat. No. 6,891,336 discloses a high-pressure discharge lamp lighting apparatus and luminaire using thereof in which a DC power operates within a pre-set frequency range such as 0˜20 KHz, 40˜50 KHz and 80˜88 KHz in order to prevent the high-pressure discharge lamp from being damaged due to resonance. In U.S. Pat. No. 6,891,336, a half-bridge inverter is used with an inductor and a capacitor to provide the high-frequency AC power to the high-pressure discharge lamp and a timing controller is used to control the pre-determined operation time in different frequency ranges in order to stabilize the output power and shorten the turn-on time. However, the “336” patent does not teach how to adjust both the frequency of the DC inverter and timing control in a continuous range.
U.S. Pat. No. 6,936,974 discloses a half-bridge inverter for asymmetrical loads that uses an operational amplifier to perform voltage control according to the reference voltage, the feedback voltage and the pre-determined upper and lower voltage limits and timing control according to the reference voltage, the feedback voltage and a pre-determined value so as to obtain a stable output power within a pre-determined range of supplied voltage and achieve over-current protection. However, the “974” patent does not teach how to adjust the frequency of the DC inverter and timing control in a continuous range externally.
Therefore, there exists a need for providing an adjustable and compact high-frequency-high-voltage power supply capable of outputting a high-frequency-high-voltage AC power at different frequencies and voltages according to different loads using external adjustments.